Design And Preparation Of Boron-based Catalysts For The Catalytic Oxidative Desulfurization Of Fuels

Recently,with the proposal of the target of“Carbon emission peak,Carbon neutrality”,fossil fuels are facing a severe challenge of transformation and upgrading from being fuel to being fine chemicals raw material.However,the presence of sulfides in fuels will lead to the poisoning of catalysts during the production process,thereby reducing production efficiency and increasing energy consumption and carbon emissions.In addition,the combustion of fuels with high-sulfur concentration will emit a large amount of sulfur oxides（SO_x）,which brings in a series of environmental pollution problems such as haze and acid rain,seriously endangering the ecological environment and human health.Therefore,it is of great significance for the sustainable development of the society and ecology to efficiently removal the sulfur compounds to achieve a clean production of fuels.In response to the shortcomings of the traditional hydrodesulfurization（HDS）technology,a series of boron-based catalysts were designed and synthesized in this research for the application of oxidative desulfurization（ODS）.The sulfur conversion of aromatic organic sulfides with molecular oxygen（O₂）as oxidant was investigated in detail to examine the catalytic activity of different catalysts.Moreover,the relationship between the catalyst structure and catalytic activity was explored to analyze the possible reaction mechanism of ODS.The main research contents and conclusions are as follows:1.An Au@BN core-shell catalyst was synthesized using hexagonal boron nitride（BN）as shell layer to enhance the thermodynamic stability of gold nanoparticles（Au NPs）.The structure and interfacial properties of the catalyst were analyzed by various characterization techniques.Adjusting different parameters such as shell thickness and calcination temperature to clarify the effect on the catalyst structure and catalytic performance.The characterization results suggest that under the optimal catalyst synthesis parameters,smaller Au NPs with a particle size of 8 nm can be obtained by this method compared to the bare Au NPs without the formation of BN outer shell.The constructed BN outer shells possess a two-dimensional porous defect structure that can provide a microchannel for the reaction substrates.Meanwhile,an interfacial interaction between the Au NPs and BN was enhanced resulted from the confinement effect,thereby further boosting the stability and catalytic activity of Au NPs.The experimental results of the ODS performance test showed that the designed Au@BN core-shell catalyst exhibited an excellent aerobic oxidation activity with a DBT conversion of 97.2%and TOF value of 546.3 h^-1 under the optimal reaction conditions.After the 10 successive runs,the conversion can still be maintained above 93.9%with a sustained Au NPs size without significant secondary growth.2.A supported platinum nanocatalyst with BN as a carrier was synthesized and a strong metal-support interaction（SMSI）between platinum nanoparticles（Pt NPs）and inert BN was constructed induced by oxidation reaction.Based on the characterization results,the successful construction of SMSI can be confirmed with the formation of boron oxide（BO_x）shell over the Pt NPs surface and the electron transfer effects detected between Pt NPs and BO_x interfaces.Importantly,the nanostructure of the Pt NPs was rearranged,contributing to the generation of under-coordinated Pt active sites.The as-prepared catalysts were applied to the ODS reaction of model system and the effect of different reaction parameters such as the loading amount of the Pt NPs,catalyst dosage and the reaction temperature on the catalytic performance were investigated systematically.A complete conversion of DBT can be achieved within 3 h under 130°C.Meanwhile,the optimized catalyst can be used to the removal of a varies sulfides.3.By introducing ionic liquids（ILs）on the surface of the Pt nanocatalysts,a modulation of interfacial electronic structure can be achieved to improve the noble-metal atom efficiency and catalytic activity.By adjusting the type of ILs,the impact of different ILs on the structure and the surface charge state of the catalyst can be determined combined with the characterizations of Raman and X-ray photoelectron spectroscopy（XPS）.The results showed that the ILs with a relatively weak electronegativity of anion can play as the electron donor to provide electrons to the Pt NPs,resulting in an electron-rich state of Pt NPs and increasing the content of the metallic Pt⁰.The modified catalysts were used for the oxidation of the organic sulfides with the O₂ as oxidant.A 97.5%conversion of DBT can be reached after reacted for 5h under 120°C.The catalyst can be regenerated through simply secondary thermal treatment.According to the electron spin resonance（ESR）and quenching experiments,the active intermediate of the reaction was determined to be the superoxide radicals.4.A carbon-doped metal-free porous boron nitride was designed with carbon spheres as both a template and carbon source.The morphology and structure of the catalyst were researched and it was observed that the introduction of carbon spheres template has successfully realized the construction of a porous thin-layer boron nitride structure,which was conducive to the exposure of active sites and enhanced the migration and diffusion of the reaction substrates.The ultraviolet-visible diffuse reflectance spectroscopy（UV-Vis DRS）and XPS were performed to analyze the chemical environment and surface charge state.The research results confirmed the incorporation of carbon atoms,which will enhance the delocalization ofπelectrons in the boron nitride structure,thus increasing the content of oxygen-containing boron sites to promote the activation of O₂.By optimizing the dosage of carbon spheres,the catalyst can acquire a complete conversion of DBT and its derivatives within 5 h.5.Based on the exploration of the catalytic active site of BN,a boron-doped metal-free nanocatalyst was prepared by a ball milling-assisted high-temperature pyrolysis method to maximize the number the active oxygen containing boron sites,thereby improving the catalytic oxidation activity.The doping sites and the coordination structure of B species were studied in detail by solid-state nuclear magnetic resonance spectroscopy（solid-state NMR）.According to the rules of the catalytic performance,it can be speculated that the structure of-B[OH…O（H）-Si]₂with the isolated B with dihydroxyl group combined with the adjacent Si-OH by hydrogen bond could be the active site of the oxidation reaction.Under the optimal condition,the as-prepared catalyst can achieve a complete conversion of DBT during 5 h at 120°C.Furthermore,it exhibited an excellent durability with a stable ODS performance above 94.8%after15 cycles,indicating that the heteroatom doping can effectively anchor the active boron sites to inhibit the hydrolysis and deactivation of the catalyst during reaction process.